1. Field of the Disclosure
The present disclosure relates to an optical communication switching system with dualized lines including an in-service line (a first optical communication line) and a detour line (a second optical communication line) as an optical communication line, and more particularly, to a technique of transferring a signal of the in-service line to the detour line without disrupting a communication service while reducing deterioration of the communication signal quality resulting from dualization of an optical transmission signal and continuing a transmission logic link.
2. Discussion of the Background Art
In order to construct an economic optical communication system, a passive optical network (PON) system in which a plurality of outdoor transmission termination device is consolidated by a single indoor transmission device has been devised (see Japanese Patent Application Laid-Open (JP-A) No. 8-102710 “Optical Transmission Device”). Thus, the cost of communication facilities has greatly been reduced, and movement of a conversion to an optical system has been under way. Further, as the transmission capacity increases like a dense wavelength division multiplexing (DWDM) or a dense time division multiplexing (DTDM), a service that requires a real time property like an image or optical telephone or a service that is high in added value has been being spread.
Conventionally, there frequently occurs a case in which a line route is forced to change due to a road widening work, a bridge replacement work, or other equipment works (a new installation or a repair of electricity or tap water) on an outdoor optical line facility (hereinafter, referred to as an interference relocating work). In this situation, when the interference relocating work on a communication facility that supports the above described service is performed, since a large amount of traffic stops at a time due to the work, influence over a number of users is immeasurable. In order to reduce the influence, for example, a work time has been divided, or the relocating work has been performed at a time zone having a small traffic amount, for example, from midnight to early morning. That is, a facility operation having low efficiency has been performed.
In such a situation, a tool for reducing a switching connection time of an optical line as much as possible and reducing a communication recovery time has been commercialized (see Japanese Patent No. 3573606 “Optical Fiber Cable Three-Point Switching Connection System”). However, it is impossible for the present system to avoid missing of transmission data or a mismatch of a transmission logic link that results from temporal separation of the optical line or an optical line length difference between the in-service line and the detour line (a phase difference of a transmission signal). Further, switching in which a switching connection time is nearly zero may be performed such that a transmission route is dualized at the time of construction of an optical line facility, and an in-service signal is previously provided from a transmission device to two routes. However, even in this case, there has been a problem in that a mismatch of a transmission logic link is unavoidable due to a route length difference.
In any case, it is unavoidable to disperse a work period so that influence (service deterioration) on a user can be minimized in view of a technical limit of such medium switching and further prolong a midnight work.
As represented by switching of a PON system, when the interference relocating work on the outdoor optical line facility is performed, services of many users should be stopped, and the influence is immeasurable. Since it is realistically impossible to match a service stop time (date and time) on many users and obtain agreement from many users, the relocating work should be performed at a time zone having a small traffic amount, for example, from midnight to early morning. Thus, there has been a problem in that a service has directly been influenced and there has been a lack of planning. Further, even in a case of a small number of users as in a single star (SS) network system, since a dedicated line in which it is actually difficult to stop a service is mostly used, the situation is not different from the PON system.
In light of the foregoing, it is an object of the present disclosure to provide an optical line switching method and apparatus of dualized lines in which phases of optical transmission signals can be matched by forming dualized lines having the same optical line length so that missing of transmission data or a mismatch of a transmission logic link can be avoided, and a service can continue.